Residences? What to Build?

Hey, I finally got the four residences in a square I've been wanting for a LONG time. Now, I dug the first layer out on three of my residences, and filled it in with a glowstone outline next to the pathway, and filled the rest with glowstone. I was thinking about getting a Dirt Remover Clock to build underground. But what could I build underground? That's why I come to you all, please give me some suggestions!